This study investigates the effect of vapor blanket duration in quenching oil on the mechanical properties and distortion of JIS-S45C carbon steel and JIS-SCM435 low-alloy steel. Four types of heat treatment oils with varying vapor blanket stage lengths were tested on key-grooved cylindrical specimens. Results indicate that quenching oils with longer vapor blanket durations produced smaller distortions, while oils with shorter durations caused larger distortions.

This work serves to expand upon the fundamental idea of high convection quenching (HCQ), examining alternative methods to destabilize vapor barrier formation in liquid quenchants. Namely, ultrasound in combination with a brine solution is applied to realize fast yet controllable quenching conditions.

This work aims to contribute to the optimization of the simulation process in the heat treatment industry. Cooling curves of a polyacrylate-based (ACR) polymer solution at a concentration of 9 and 12 %, using an axial flow rate of 1.30 L/min on an immersion system and a fluid temperature of 45 °C were acquired and analyzed. Air quenching was also used to compare the polymer quenching conditions.

This paper reviews several techniques for hardness prediction, from simple to complex, and compares the calculated results to those published previously. Using “old-school” methods based on the Grossman H-Value and Lamont charts, we predict the expected hardness for SAE 1045 and SAE 6140 round bars in three sizes: 1, 3, and 5 in. (25, 75, and 125 mm).

Gas carburizing with quenching is one of the most useful heat treatment processes for steel parts. However, after quenching distortion is still occurs. The nitriding and nitrocarburizing are the surface hardening heat treatment methods with low distortion, but these methods require the long treating time to obtain a thick hardened layer. Austenitic nitriding and quenching (ANQ) solves these problems. In ANQ process, nitrogen is infiltrated into the steel parts in austenite phase, and they are quenched to harden. The ANQ process can also be applied to cheap low carbon steel such as the Cold Rolled Carbon Steel Sheet. In this study, the effect of ANQ on mechanical properties was examined. For infiltrating the nitrogen into the steel parts, the steel parts were heating to 750°C or higher in an ammonia atmosphere and heating to 750°C or higher in a nitrogen glow discharge. After the ANQ process, hardness profiles, structure, nitrogen and carbon concentration profiles were observed. Also, distortion, tribological properties, impact value and fatigue strength were examined. The effective case depth, which is treated by ANQ, is larger than the effective case depth of gas nitrocarburizing for same period of time. Distortion of ANQ is much smaller than that of gas carbonitriding, and it is almost equal with that of gas nitrocarburizing. The seizure load is same as with other surface hardening heat treatment processes. The wear loss of ANQ is a lower, in the amount of about 1/2 that of the carbonitrided specimen and 1/3 that of the gas nitrocarburized specimen. The ANQ is an effective heat treatment process for parts which require wear resistance. The tempering softening resistance is improved by nitrogen infiltration. ANQ also improves the impact value and fatigue strength.

Carbide free bainitic microstructures can be developed via different thermal processing routes, and the details affect the scale and morphology of the microstructural constituents. In this study, bainitic microstructures are formed by either a controlled cooling process or an austempering process to evaluate the relationship between microstructure and mechanical properties in a 0.2C - 2Mn - 1.5Si - 0.8Cr steel containing small amounts of Nb, Ti, B, and N, and the results are compared to a 4140 steel processed via quenching and tempering. The resulting microstructures are characterized with scanning electron microscopy. When compared to microstructures produced via austempering, microstructures produced with a controlled cool exhibit an increased variety of transformation products, specifically regarding size and distribution of martensite-austenite constituents within a lath-like bainitic ferrite matrix. Nanoindentation testing shows that different transformation products exhibit significantly different local hardness. In all (primarily) bainitic conditions tested for these materials, the martensite/austenite constituent exhibits the highest hardness, followed by the lath bainitic ferrite/retained austenite constituent. Granular bainite and coarse bainitic constituents exhibit the lowest relative hardness in the conditions where they are observed.

Decarburization of steel parts during heat treating results in a lower surface hardness, undesirable residual stress profiles, and poor part performance. Significant effort has been made towards preventing decarburization and determining the impact of annealing time and temperature on decarburization rate. Much of the published research has focused on medium carbon steels, ranging from 0.3wt% C to the eutectoid composition. The goal of the current research is to determine decarburization rates for steels with carbon concentrations above the eutectoid concentration. AISI 52100 steel was heated in air for 12, 24, and 36 hours at three temperature ranges (below A 1 , above A cm , and between A 1 and A cm ). Optical microscopy was used to determine the carbon concentration as a function of depth from the surface. The diffusion coefficients of carbon in austenite and ferrite plus cementite phase assemblages were calculated. These diffusion coefficients can be used in a finite difference simulation to predict decarburization at different temperatures and times.

Quenching and tempering (Q&T) allows a wide range of strength and toughness combinations to be produced in martensitic steels. Tempering is generally done to increase toughness, although embrittling mechanisms result in temperature ranges where strength and toughness may decrease simultaneously. Tempered martensite embrittlement (TME) represents one such mechanism, associated with the decomposition of retained austenite and precipitation of cementite during tempering, usually between 250 and 450 °C. The use of induction heating allows for time-temperature combinations, previously unobtainable by conventional methods, that have been shown to improve properties. The present work shows a beneficial effect of rapid tempering in alloy 1045, with an increase in energy absorption of about 50% when measured at room temperature via a three-point bending fracture test in the TME regime. Phase fraction measurements by Mössbauer spectroscopy showed that increased energy absorption was obtained despite essentially complete decomposition of retained austenite during tempering. Scanning electron microscopy (SEM) investigation of the carbide distribution showed refinement of the average carbide size of approximately 15% in the rapid tempered conditions. SEM characterization of the fracture surfaces of the rapid tempered three-point bend samples showed that, despite an increase in energy absorption in the TME regime, increased microscopic ductile fracture appearance was observed only at the highest test temperature.

This study investigates the heat treatment response and microstructure evolution of high-carbon steels for additive manufacturing. Moreover, the role of nitrogen as an interstitial alloying element is addressed. Stainless steel 440C, cold-work D2, hot-work H13, and T15 high-speed tool steel overspray powders from spray forming were investigated. The thermal behavior of these materials was examined using a thermal analyzer that combines calorimetry and thermogravimetry. Additionally, interstitial alloying with nitrogen was performed in-situ to understand its influence on thermal behavior. The (near-)equilibrium nitrogen solubility in 440C and D2 in contact with flowing N 2 gas was recorded as a function of temperature through the interval 1200 to 800 °C. The microstructure of the steel powders was characterized by light optical microscopy and X-ray diffraction. The potential of nitrogen alloying and the importance of optimized heat treatment protocols are emphasized with respect to high-carbon steels in additive manufacturing applications.

Carburizing is frequently utilized in the automotive industry in order to increase the surface hardness of a steel alloy while retaining toughness and ductility in the core. At elevated temperatures where some carburizing processes are performed, abnormal grain growth (AGG) can occur. During AGG, the microstructure undergoes bimodal grain growth with some grains growing exponentially faster than others. The growth of large austenite grains through AGG compromises the fatigue performance of carburized steels. AGG is further exacerbated by cold work introduced into the alloy prior to carburizing. Warm work is also sometimes utilized in part forming prior to carburizing. In this study, the effects of warm work on AGG were investigated. AISI 4121 and a modified AISI 4121 that contains Nb and Mo microalloying additions rather than Al for grain size control were warm worked in a range of 0-50% at a temperature of 900°C and then heated in a furnace for various lengths of time at a temperature of 930 °C to simulate a carburizing thermal history. The average prior austenite grain size (PAGS) tended to decrease as the degree of warm work increased, with the NbMo-modified alloy presenting a finer PAGS at all percentages of warm reduction and different lengths of time at the simulated carburization temperature. Specimens of the 50% warm reduced condition were also cold rolled at 5, 10, and 25% reductions, typical of cold sizing, prior to simulated carburization. The average PAGS of these CR samples was finer than their 0% CR counterparts, but the PAGS increased with CR in the modified alloy after 328 minutes of simulated carburization.

Carburizing and induction hardening are two commonly used surface heat treatments that increase fatigue life and surface wear resistance of steels without sacrificing toughness. It is hypothesized that induction hardening following carburizing could yield further increased torsional fatigue performance through reducing the magnitude of the tensile residual stresses at the carburizing case-core interface. If successful, manufacturers could see gains in part performance by combining both established approaches. A carburizing heat treatment with a case depth of 1.0 or 1.5 mm and an induction hardening heat treatment with a case depth of 0, 2.0, or 3.0 mm were applied to torsional fatigue specimens of 4121 steel modified with 0.84 wt pct Cr. The carburized samples without further induction processing, the 0 mm induction case depth, served as a baseline for comparison. The as-received microstructure of the alloy was a combination of polygonal ferrite and upper bainite with area fractions of approximately 27% and 73% respectively. The case microstructure of the heat-treated conditions was primarily tempered martensite and transitioned to a bainitic microstructure around the deepest overall case depth. Material property characterization consisted of radial cross-sectional hardness testing and torsional fatigue testing. The hardness profiles confirmed that the designed case depths were achieved for all conditions. Torsional fatigue testing was conducted using a Satec SF-1U Universal Fatigue Tester. Of the six tested conditions, the condition with the deepest case depths, i.e. carburized to 1.5 mm and induction hardened to 3.0 mm, was expected to have the greatest increase in fatigue performance. However, initial fatigue results potentially indicate the opposite effect as the non-induction hardened samples exhibited longer fatigue lives on average.

Quenched and tempered (Q&T) medium-C steels with various V and Mo additions were studied to understand the relationship between alloy carbide precipitation and hydrogen absorption and trapping behaviours. Heat treatments were selected in the temperature range favourable for V carbide formation, 500-600 °C, leading to higher hardness compared to similar V- and Mo-free alloys due to precipitation hardening. Heat-treated coupons were electrochemically charged to introduce hydrogen, and the bulk hydrogen concentration was measured using melt extraction analysis. Hardness and dislocation density were measured for each tempered condition to relate these properties to the hydrogen absorption and trapping behaviours of each material. Results indicate that dislocation density as well as V and Mo carbide precipitation increase the extent of hydrogen absorbed during charging and the amount of hydrogen remaining trapped after holding at ambient temperature for up to 168 h (1 week).

The objective of this work was conducted to investigate the influence of nickel (Ni) content and retained austenite on rolling-sliding contact fatigue (RSCF) life in carburized gear steel. In order to evaluate Ni and retained austenite effects, this study utilized carburized steel specimens of 4120 (0.13 wt pct Ni) and 4820 (3.38 wt pct Ni), which were subjected to RSCF testing. The specimens were gas carburized with a resulting case depth of approximately 1.3 mm, based on a hardness of 500 HV. The retained austenite was measured using x-ray diffraction at depths beneath the surface of 50, 250, 450, 650 μm. The 4120 specimens have a higher surface retained austenite content than the 4820. Specimens were surface ground to an average surface roughness of 0.2 μm to decrease the effect of as-carburized surface roughness on the fatigue life. The specimens underwent RSCF testing, with a surface contact stress of 2.5 GA and a slide to roll ratio of -20 pct, until a pit formed, as detected by an accelerometer. The pits that formed on the surface of the specimens were analysed with secondary electron microscopy, macrophotographs, and light optical microscopy. The pits that formed from the RSCF testing conditions were surface-initiated. The fatigue life of the 4820 specimens was higher than the fatigue life of the 4120 specimens, suggesting that the higher Ni level is beneficial to the fatigue life.

Induction hardening is used to harden small cylinders of SAE 1074 steel. Parts were quenched with a high concentration of a polyalkylene glycol (PAG) type quenchant. Soft spots were found on a small percentage of the parts. These soft spots were consistently at one location about 2/3 from the bottom of the part. These soft spots were circular, and consistent in size. The product was examined and determined to be adequate and to specification. Using a lower concentration of quenchant, the quench speed was increased. While this reduced the number of soft spots, it did not eliminate the soft spots. Faster quenches were tried with similar results. Using Transvalor SIMHEAT, we were able to duplicate the results, and eliminate the source of soft spots.

The phase transformation model is coupled with the inverse heat conduction problem (IHCP) to estimate the steel/quenchant interfacial heat flux. Cylindrical steel probes having section thicknesses 25 and 50mm, respectively, and lengths 30mm were made from medium and high carbon steels (AISI 1045 and 52100). The probes were quenched in mineral, neem, and sunflower oils. The cooling curves at the centre and near the surface of steel probes were recorded. The near-surface cooling curve was used as a reference temperature data in the IHCP algorithm for the estimation of surface heat flux, whereas the cooling curve at the centre was used as the boundary condition of the axisymmetric model of the probe. The effect of phase transformation on the metal/quenchant interfacial heat flux was indicated by a kink and rise of heat flux. The increase in the section thickness of the probe from 25 to 50mm decreased the magnitude of the heat flux. Increasing section thickness increases the phase transformation, increasing the resistance to heat flow at the metal/quenchant interface.

Archaeological digs have found many types of knives, with varying quality of steel and microstructure. Typically, these steels are carbon steels with carbon contents on the order of 0.60%. Historically, there have been many myths concerning the quenchants used by ancient blacksmiths in the heat treatment of swords and knives. Various liquids have been cited in the archaeometallurgical literature as quenchants. Each of these quenchants is supposed to extend to the knife special and even mythical properties. However, none have been examined for cooling curve behavior. In this paper, various quenchants are examined for typical heat transfer, and microstructure is predicted for simple steels commonly used in ancient knife making.

Heat-treatment simulation is a powerful tool for gear design and process troubleshooting, but many times the predicted gear distortion is difficult to compare to physical gear measurements and to required specification charts or measurements. To help ease this burden, two software programs are utilized to provide powerful gear analyses to heat-treatment simulation results. This paper briefly describes the software used, DANTE and Integrated Gear Design (IGD), and presents a simple case study. The stress and deformation from the heat treatment of a small gear made of SAE 10B22 are predicted using DANTE. The distorted gear geometry is then imported into IGD and the predicted distortion is compared to the actual measurements of the gear.

Powder metallurgy (PM) is the fabrication process of compacting metal powders to shape and sintering these compacts to yield the final material’s properties. The PM compaction process allows for complex geometries to be formed that would normally lead to long and expensive machining processes from wrought steels. Special alloy selection can allow for hardening of the microstructure during the sintering procedure. The sinter hardened (SH) alloys exhibit good mechanical properties along with good hardenability and dimensional stability and may be a suitable replacement for wrought steels where low distortion from heat treatment or microstructural control is required. In this study, it was found for a complex geometry coupler application, a SH alloy could successfully replace an austenitizing heat treatment process with a low carbon steel. The low carbon steel was found to have micro heterogeneities from heat treatment that lead to premature failure in the application. Dimensional distortion and production variance were also of concern with the low carbon steel. The SH material demonstrated acceptable physical properties, hardness and microstructural uniformity to solve the concerns associated with processing of the low carbon steel coupler. Post processing optimization also added to the life performance of the coupler by tailoring the final microstructure to mating components.

Commercially, carbon steels are induction heated at heating rates on the order of 100 to 1,000 °C·s -1 for surface hardening. The high precision DIL 805L dilatometer employs induction heating and is often used to study transformation characteristics and prepare test specimens for metallurgical analysis. However, heating the commonly used 4 mm diameter by 10 mm long specimens at rates above 50 °C·s -1 results in non-linear heating rates during transformation to austenite and large transient temperature variations along the specimen length. These limitations in heating rate and variances from ideal uniform heating can lead to inaccurate characterization of the transformation behavior compared to commercial induction hardening practices. In this study it is shown that changing the specimen design to a thin wall tube allows faster heating rates up to 600 °C·s -1 and modifies the pattern of temperature variations within the test sample. The response of selected specimen geometries to induction heating in the dilatometer is characterized by modelling and tests using multiple thermocouples are used to verify the models. It is demonstrated that the use of properly designed tubular test specimens can aid in more accurately establishing transformation characteristics during commercial induction hardening.

AISI 52100 is a high carbon alloy steel typically used in bearings. One hardening heat treatment method for AISI 52100 is austempering, in which the steel is heated to above austenitizing temperature, cooled to just above martensite starting (Ms) temperature in quench media (typically molten salt), held at that temperature until the transformation to bainite is completed and then cooled further to room temperature. Different austempering temperatures and holding times will develop different bainite percentages in the steel and result in different mechanical properties. In the present work, the bainitic transformation kinetics of AISI 52100 were investigated through experiments and simulation. Molten salt austempering trials of AISI 52100 were conducted at selected austempering temperatures and holding times. The austempered samples were characterized and the bainitic transformation kinetics were analyzed by Avrami equations using measured hardness data. The CHTE quench probe was used to measure the cooling curves in the molten salt from austenitizing temperature to the selected austempering temperatures. The heat transfer coefficient (HTC) was calculated with the measured cooling rates and used to calculate the bainitic transformation kinetics via DANTE software. The experimental results were compared with the calculated results and they had good agreement.